1. Field of the Invention
This invention relates to spacer rings for placement between hard tubular elements that are interfit, one within the other, to facilitate relative shifting therebetween and, more particularly, to a ring formed from matted metal threads.
2. Background Art
There are many high temperature environments in which tubular metal elements/pipes are joined together by mating, one within the other. One exemplary environment is an automobile exhaust system wherein several of the exhaust components are so interconnected.
One problem that has plagued the automobile industry is that of noise generation between the mated tubular elements on the exhaust system. Differences in the heating and cooling rates for the cooperating elements can cause relative shifting and rubbing together of adjacent hard metal surfaces thereon, which can generate significant noise.
It is known to employ a spacer element to maintain a predetermined gap between the facing surfaces to accommodate expansion and contraction of the elements, without rubbing therebetween, through the contemplated operating temperature range. One conventional spacer consists of a ring of wire mesh interposed between the radially outwardly facing surface of the inner element and the radially inwardly facing surface of the outer element. This mesh material is made from a relatively heavy gauge, woven wire. The formed ring is bonded to the inner element, as by welding.
There are several drawbacks with the above wire mesh spacer ring. First, the wire defining the mesh is sufficiently rigid that the ring is virtually incompressible. Consequently, the ring lacks the flexibility necessary to accommodate dimensional variations in the elements resulting from temperature changes.
A further drawback with the wire mesh ring of the prior art is that the wire of the mesh is so rigid that it is virtually impossible to accurately conform the ring to the surfaces of the inner and outer elements between which it is interposed. The result is that certain points of the ring are rubbed against the inner surface of the outer tube and themselves produce an undesirable grating noise when the elements shift.
A further problem with the prior art mesh ring results from spot welding, which is the process generally used to affix the ring to the inner element. The spot welds deform the ring from its desired cylindrical configuration. The result is a reduction in the contact area between the ring and facing surfaces of the elements and considerable noise production when the elements shift.
Further, the wire mesh, because of its inability to conform to and fill the region between the tubes, leaves a gap for the transmission of sound waves. This problem is aggravated in the regions surrounding the welds.
Another attempted solution to the above problem has been the provision of a radially projecting dimple on one of the inner and outer elements. The dimple maintains a desired spacing between the inner and outer elements. However, the dimple, as with the wire mesh ring, rubs undesirably on the surface against which it bears and itself creates noise when the elements shift relative to each other.